Ionic amplifier



Jan. 29, 1935. s, RUBEN 101m; AMPLIFIER Filed May 5, 1933 R O T N E v Ml/EL ATTO R N EY Patented Jan. 29, 1935 IONIC AMPLIFIER Samuel Ruben, New Rochelle, N. y.

' Application May 5, 1933, Serial No. 009,50:

24 Claims.

This invention relates to an ionic dischar e amplifier device. This application is a continuation in part of my applications Serial Number 634,994, filed 27, September 1932, and Serial Num- 5 her 641,334 filed'5 November, 1932 and describesan improvement over the devices of those applications.

An object of the invention is the provision of an ionic discharge device capable of being used as an amplifier.

Another object is to provide a means of obtaining a sensitive or graduated control of an ionic discharge throughout the entire current output range.

A specific object is to obtain such control by the use of a negatively biased grid element, so that an electrostatic control may be had with no or negligible grid current flow.

A further object is the provision of an amplifier device in which a higher power output is obtained by the use of an ionized metal vapor such as mercury, and controlled by an electronic discharge within the amplifier device. v

An object is to provide an electrical discharge tube allowing a lower plate load impedance and a power output and sensitivity greater than has heretofore been obtained in amplifier tubes.

Other objects will be apparent from the disclosure and from the drawing in which,

Fig. 1 shows a tube of the invention in an operable circuit and Fig. 2 is a top view, showing the arrangement of the elements.

The tube may also be used in other circuits and for such other uses as combined oscillator and detector, audio and radio frequency amplifier, voltage amplifier in connection with such devices as photo cells, relays, etc.

In thermionic discharge tubes of the prior art employing a thermionic cathode in a space charge reducing atmosphere such as mercury, only a trigger type of control is obtained. Once the current fiow starts, the grid has little influence on the discharge, the change in grid voltage merely varying the thickness of the sheath of positive ions surrounding the grid. Where the grid supply potential variations are of a practical order, the plate potential must be disrupted to extinguish the discharge. The trigger potential is determined by the initial amplification factorof the tube. This trigger characteristic has prevented the use of tubes of this type in circuits such as shown in the drawing or in other audio amplifier circuits.

In the tube of my invention, a complete grad- PATENT omen,

uated and sensitive control, equivalent to that obtained in a pure electron type of discharge is obtained. In this tube, the relatively pure electron discharge surrounding the cathode is directly controlled within the "cathode fall space and the control means is electrostatically shielded from an ionic current emanating from the positive ion sheath which exists beyond that point. An important feature of the tube is the high plate potential which can be applied-for I0 instance, 250 volts, which is many times the ionization potential of mercury vapor. This allows a high power output, especially when the low plate circuit impedance of the tube is considered.

The invention employs a novel relationship be- 15 tween a cathode, a control grid, an electrostatic shielding or bufier electrode and an anode, within an ionizable medium, such as mercury. It is based upon the following: That electrons emitted or driven from a cathode into an ionizing atmosphere must travel a certain distance to reach a I critical velocity equal tothe ionization potential of the surrounding atmosphere, before ionization by impact occurs, with consequent production of ions which reduce the space charge and allow a low cathode-anode drop of potential. The dense electron space or area between the cathode and the point at which the electrons have reached a velocity sufiicient to ionize the surrounding atmosphere is known as the cathode fall space. If

an electrostatic control element, such as'a negatively biased grid, be positioned no farther from the cathode than the cathode fall space limits and preferably located within that space, a graduated current control of the ionized discharge is obtained. The control grid should be shielded or surrounded by another control member which is positively biased in order to prevent an ionic cur.- rent flow to the negatively biased control grid when an ionic discharge takes .place. The electrical discharge should be confined to the space directly between the cathode emitting surface and the anode through the grid turns.

In general, the device operates with a direct electrostatic control of an electron discharge with means of electrostatically shielding the control electrode from an ionic discharge resulting from impact of the controlled electron discharge with the vapor atmosphere at a distance greater than the distance between the cathode and control grid. I

Essentially, the tube employs two distinct forms of discharge within the same envelope, namely, a pure electron portion for control and a positive.

ion portion for space charge reduction. The only way in which two such discharges can be used in the same envelope is by operating the control electrode within the distance or space closely adjacent to the cathode in which no positive ionization of the atmosphere occurs.

Further, the graduated control can only be eillciently or practically effected by a control electrode or grid within the electron area if the grid is completely electrostatically shielded from a flow of ions from the area beyond. This is especially so, because to eiliciently or practically eil'ect a control of an electron discharge, a negatively biased grid must be used. Thus, without the electrostatically shielding electrode, the control grid would serve as a discharge electrode for the positive ions generated beyond the cathode fall space and a grid current would flow, reducing or eliminating the control potential of the negatively biased grid electrode.

In the development of the device, certain important factors in relation to construction and operation of the tube have been determined. These may be stated as follows: The inner side of the control grid should be no farther from the cathode'than the limits of the cathode fall space and should preferably be within that area. This space (cathode fall space) varies with such factors as current density, ionization potential of the ionizable medium, anode potential, cathode temperature, bulb temperature, internal atmospheric (tube) pressure and cathode electron emissivity. However, practical values can be stated in terms of suggested limits, that is, for a power detector tube, capable of directly supplying several watts audio frequency from a modulated radio frequency supply potential, the control grid should be spaced .007" to .015 from the cathode, an average spacing being about .010". A grid which is wound with wire having a diameter of about .005" .should have about 28 to 36 turns per inch with an average of 32 turns. If the number of turns of the grid wire is increased beyond the values given, an increase in plate impedance is obtained or if reduced, the tube becomes unstable in operation at higher power outputs, with consequent leakage anduncontrolled currents, especially when the vapor pressure of the mercury increases due to temperature rise. If a smaller diameter grid wire is used, the number of turns may of course be increased. In this way, also, it is possible to further vary the impedance and increase the efficiency of the tube.

The cathode outside diameter for such a tube would be in the order of .130" the cathode length would be .625" of which .375" would be coated with an emission material. The inside diameter of the control grid would be .150" and that of the shielding electrode or grid .190".

The shield grid is preferably mounted as close as practicable to the control grid and in general should be located at a distance less than the mean free path length of the ionizing medium so that no ionic discharge can be maintained between the two electrodes when at a potential difference. Except for the diameter difference, the construction of the shielding electrode or grid should correspond to that of the control grid. It is desirable that each should have the same number of 'tums. The negative bias on the control grid and the positive bias on the shield or buffer grid are determined applied.

By locating the electrostatically shielding grid close to the control grid, the limits of the cathode by the plate potential fall space are widened, the un-io'niaed area being extended. This also facilitates tube production by allowing an increase in the diameter of the control grid, thus obviating the necessity of too close a spacing between cathode and grid.

The surrounding anode is naturally located far beyond the cathode fall space and at a distance from the shielding electrode greater than the mean free path length of the electrons in the ionizable medium. The anode is preferably corrugated when higher power output isdesired and it may also be tapered upward.

In order to prevent an ionic discharge other than directly in the space between the cathode and anode, insulating plates are fastened over the ends of the anode. These also serve to keep the elements in place.

Thesize of the bulb or tube should be such as to allow the device to reach equilibrium temperature within a reasonable time.

Summarizing the important factors found necessary for eflicient operation, it may be stated,

1. The space between the cathode and control grid should not be greater than the cathode fall space (in relation "to the ionizable medium used).

2. The electrostatically shielding electrode should be positioned as close as possible to the control grid so that no substantial ionization can occur in the space between these two electrodes.

3. The anode should be spaced at a distance from the cathode greater than the cathode fall space distance.

4. The space between the turns of or the openings in the control grid should not be wide enough to allow uncontrolled electron emission to discharge therethrough.

5. The space between the turns of or the openings in the shielding electrode should not be wide enough to allow any substantial discharge of ions therethrough. (It has been found experimentally that spaces of the same order as those of the control grid are satisfactory.)

6. The discharge should be confined directly to the space between the cathode emitting surface and the anode through the grid turns.

In order to afford a detailed description of one embodiment of my invention, reference is made to the accompanying drawing. In Fig. 1 the blackened tube (1) houses cathode (2) which is coated with strontium and barium oxides (2a) to provide electron emission and which is almost entirely closed at the top to retain the heat. The cathode is supported by lead terminal (2b). Closely surrounding the cathode is control grid (3) supported by lead (322) and support (30) and which has an inside diameter about ten mils greater than that of the outside diameter of the cathode. It has a winding of 32 turns per inch along the cathode axis and extends for the length of the cathode emission surface. Surrounding this at a distance of approximately .015" is shield grid (4) which has the same number of turns as grid (3) but of a wider diameter. Grid (4) is supported by lead (4b) and support (40) The nickel anode (5) is of .750 diameter and at its terminals appear mica discs (7) and (8) for confining the discharge to the space between the cathode and anode and which help to maintain the elements in place. The mica discs are held in position by fasteners (7a) and (8b) The cathode is heated by tungsten heater wire (6) which has an integrally formed coating of aluminum oxide to insulate it from the cathode. The capsule (9) contains mercury and a getter such as magnesium. (RF) is the radio frequency input source, energy from-which is applied to the grid (3) and cathode (2) through the negative biasing portion of resistance (R) which is shunted across plate potential supply (Ep), allowing a positive bias potential to be applied to shield grid (4) At (C) is the output condenser for the anode potential supply and at (S) a translating device, such as a loud speaker.

I prefer to use mercury vapor as the ionizing medium, although other monatomic gases such as neon, argon or helium'can be used. The mercury may also contain a small amount of sodium or potassium.

While the cathode shown is indirectly heated, a directly heated type may, of course, be used.

The assembled tube should be completely de- Easified and the alkaline earth oxides broken down to their active form as is general practice, the magnesium getter and the mercury pill then being discharged into the tube. 1

In operation, the cathode (2) is raised to emission temperature, and electrons are discharged therefrom. Until these reach a potential equivalent to' the cathode fall space distance, they do not ionize the mercury vapor. The control grid (3) exerts an electrostatic control on the electrons within the cathode fall space and is negatively biased so that the plate current is held at a low value. The shield grid (4) is positively charged to prevent ionic currents from discharging to the control grid and to reduce initial tube impedance. When a modulated radio frequency potential is applied to the grid circuit, there is a large plate current flow in proportion to the positive half of the supel sed radio frequency oscillation. As this control is of a uniformly graduated nature, a rectified reproduction in the plate circuit occurs. A power output many fold that obtainable in a pure vacuum tube of equivalent structure is obtained and with increased sensitivity. As so used, the tube permits the operation of radio receivers without the use of audio amplifier tubes.

If the tube is used for audio frequency oscillations, the control grid is biased up to a point at which a minimum distortion occurs.

Since certain changes in carrying out the construction of the tube and its components and obvious substitutions can be made in the arrangement of the elements and in the materials without departing from the scope of the invention, such as placing two or more amplifier units in one envelope, substituting perforated or slotted control and shielding electrodes for the wound type described, etc., it is intended that all matters contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. An ionic discharge amplifier comprising a sealed envelope containing an ionizable medium, a cathode having an electron emission surface, a control grid surrounding said cathode along its length and positioned at a distance therefrom no greater than the limits of the space of controllable cathode electron emission, another grid surrounding said control grid along its length for shielding the control, grid from a positive ion sheath, anode surrounding said cathode and grids along their length and spaced at a distance from the outergrid sufficient to allow ionization in the space therebetween, and means at the ends of the cathode electron emission area to direct andconflne the electron discharge through the control grid. I

2. An ionic discharge amplifier as described in claim 1 in which the control grid is adapted to be negatively biased in respect to the cathode.

3. An ionic discharge amplifier as described in claim 1 in which the shielding grid is adapted to be positively charged in respect'to the cathode and control grid.

4. An ionic discharge amplifier as described in claim 1 in which the grids are of the wire wound type.

5. An ionic discharge amplifier as described in claim 1 in which the ionizable medium is a mercury amalgam.

6. An ionic discharge amplifier comprising a sealed envelope containing an ionizable medium, a cathode having an electron emitting surface, an anode, a wire wound control grid surrounding said cathode along its length and positioned within the controllable portion of the discharge between said cathode and anode, another wire wound grid surrounding said control grid and being adapted to be charged positively in respect thereto, with insulating means attached at the ends of said electrodes so as to confine the electrical discharge directly to the space between the cathode and anode through the spaces between windings of said grid elements.

.7. An ionic discharge device comprising a thermionic electron emission cathode, a control grid and an anode, within an ionizable medium, said control grid being positioned at a distance from the cathode no greater than the cathode fall space of said ionizable medium, and an electrostatic means positioned between said anode and control grid for shielding said control grid from a positive ion sheath, the anode being positioned at a distance from the cathode greater than the cathode fall space.

8. An ionic discharge device comprising a thermionic electron emission cathode, a control grid and an anode, within an ionizable medium containing mercury, said control grid being positioned at a distance from the cathode no greater than the cathode fall space of said ionizable medium, and an electrostatic means positioned between said anode and control grid for shielding said control grid from a positive ion sheath, the anode being positioned at a distance from the cathode greater than the cathode fall space.

9. An ionic discharge device comprising a thermionic electron emission cathode, a control grid and an anode, within an ionizable medium, said control grid being positioned at a distance from the cathode no greater than the cathode fall space of said ionizable medium, and an electrostatic means positioned between said anode and control grid for shielding said control grid from a positive ion sheath, the anode being positioned at a distance from the cathode greater than the cathode fall space, and means for confining the discharge to the space between the cathode and anode. I

10. An ionic discharge device comprising va thermionic electron emission cathode, a wound control grid and an anode, within an ionizable medium, said control grid being positioned at a distance from the cathode no greater than'the cathode iall space of said ionizable medium, a second wound grid positioned. between said anode and control grid for shielding said control grid from a positive ion sheath, the anode being positioned at a distance from the cathode greater than the cathode tall space, and insulator blocking members positioned at the anode terminals for confining the discharge to the space between the cathode and anode.

11. An ionic discharge amplifier comprising a sealed envelope containing an ionizable medium,

' an anode, a thermionic emission cathode, a concathode fall space.

12. An ionic discharge amplifier comprising a sealed envelope containing an ionizable medium,

an anode, a thermionic emission cathode, a control grid positioned at a distance from the oathode no greater than the cathode fall space limit of said ionizable medium, and an electrostatic means interposed between said control grid and anode for shielding said control grid from a positive ion sheath, said electrostatic means being positioned at a distance from the control grid no greater than the mean free path length of the ionizable medium, the anode being positioned at a distance from the cathode greater than the said cathode fall space.

13. An ionic discharge amplifier comprising a sealed envelope containing a monatomic gas atmosphere, an anode, a thermionic emission cathode, a control grid positioned at a distance from the cathode no greater than the cathode fall space limit of said monatomic gas, and an electrostatic shielding means interposed between said control grid and anode for shielding said control grid from a positive ion sheath, said shielding means being positioned close enough to the control grid to prevent the occurrence of any substantial ionization in the space between the control grid and shielding means, the anode being positioned at a distance from the cathode greater than the said cathode fall space.

14. An ionic discharge amplifier comprising a sealed envelope containing mercury vapor, an anode, a thermionic emission cathode, a control grid positioned at a distance from the cathode no greater than the cathode fall space limit of said mercury vapor, and an electrostatic shielding means interposed between said control grid and anode for shielding said control grid from a positive ion sheath, said shielding means being positioned close enough to the control grid to prevent the occurrence of any substantial ionization in the space between the control grid and shielding means, the anode being positioned at a distance from the cathode greater than the said cathode fall space.

15. An ionic discharge amplifier comprising a sealed envelope containing an ionizable medium, an anode, a thermionic emission cathode, a control grid positioned at a distance from the oathode no greater than the cathode fall space limit of said ionizable medium, and an electrostatic shielding means interposed between said control grid and anode for shielding said control grid from a positive ion sheath, said shielding means being positioned close enough to the control grid to prevent the occurrence of any substantial ionization in the space between the control grid and shielding means, the anode being positioned at a distance from the cathode greater than said cathode fall space, and means for confining the discharge to the space between the cathode and anode. I Y

16. An ionic discharge amplifier comprising a.

sealed envelope containing an ionizable medium, an anode, a. thermionic emission cathode, a control grid positioned at a distance from the oathode no greater than the cathode tall space limit of said ionizable medium, and an electrostatic shielding means interposed between said control grid and anode ior shielding said control grid from a positive ion sheath, said shielding means being positioned close enoughto the control grid to prevent the occurrence of any substantial ionization in the space between the control grid and shielding means, the anode being positioned at a distance from the cathode greater than the said cathode fall space, and insulator blocking members positioned at the anode terminals for confining the discharge to the space between thev cathode and anode.

17. An ionic discharge amplifier comprising a sealed envelope containing an ionizable medium, an anode, a cathode and a control grid encircling said cathode along its emission length and positioned at a distance from the cathode no greater than the cathode fall space of said ionizable medium, and an electrostatic shielding means interposed between said control grid and anode ior shielding said control grid from a positive ion sheath, said control grid having openings insufiicient to allow the substantial discharge therethrough of any uncontrolled electron emission, the anode being positioned at a distance from the cathode greater than said cathode fall space.

'18. An ionic discharge amplifier comprising a sealed envelope containing an ionizable medium, an anode, a cathode and a control grid encircling said cathode along its emission length and positioned at a distance from the cathode no greater than the cathode fall space of said ionizable medium,-and an electrostatic shielding means interposed between said control grid and anode for shielding said controlgrid from a positive ion sheath. said electrostatic shielding means having openings insufficient to allow a substantial ionic discharge therethrough, the anode being positioned at a distance from the cathode greater than said cathode fall space.

19; An ionic discharge amplifier comprising a sealed envelope containing an ionizable medium, an anode, a cathode, a wound control grid encircling said cathode along its emission length and positioned at a distance from the cathode no greater than the cathode fall space of said'ionizable medium and an electrostatic means interposed between said control grid and anode for shielding said control grid from a positive ion sheath, the spaces between the turns of said control grid being insufiicient to allow the discharge therethrough of any uncontrolled electron emission, the anode being positioned at a distance from the cathode greater than the said cathode fall space.

20. An ionic discharge amplifier comprising a sealed envelope containing an ionizable medium, an anode, a cathode, a wound control grid encircling said cathode along its emission length and positioned at a distance from the cathode no greater than the cathode fall space of said ionizable medium and an electrostatic means interposed between said control grid and anode for shielding said control grid from a positive ion sheath, the spaces between the turns of said control grid being substantially not greater than twice the cathode fall space length, the anode being positioned at a distance from the cathode greater than said cathode fall space.

21. An ionic discharge amplifier comprising a sealed envelope containing an ionizable medium, an anode, a thermionic emission cathode, a control grid positioned at a distance from the cathode no greater than the cathode fall space limit of said ionizable medium and being located at a distance from the cathode substantially not greater than .015", and an electrostatic shielding means interposed between said control grid and anode for shielding said control grid from a positive ion sheath, said shielding means being positioned close enough to the control grid to prevent the occurrence of any substantial ionization in the space between the control grid and shielding means, the anode being positioned at a distance from the cathode greater than said cathode fall space.

22. An ionic discharge amplifier comprising a sealed envelope containing an ionizable medium, an anode, a thermionic emission cathode, a control grid positioned at a distance from the cathode no greater' than the cathode fall space limit of said ionizable medium and an electrostatic shielding means interposed between said control grid and anode for shielding said control grid from a positive-ion sheath and being located at a distance from the control grid substantially not greater than .015", the anode being located at a distance from the cathode greater than said cathode fall space.

23. An ionic discharge amplifier comprising a sealed envelope containing an ionizable medium, a thermionic emission cathode, a wound control grid encircling said cathode along its emission length and positioned at a distance from the cathode no greater than the cathode fall space of said ionizable medium, a wound electrostatically shielding electrode encircling saidcontrol grid and being spaced close enough thereto to prevent the occurrence of any substantial ionization in the space therebetween, said shielding electrode and said controlgrid having approximately the same number of turns, and a tubular anode surrounding said cathode, control grid and shielding electrode, said anode being positioned at a distance from the cathode greater than the said cathode fall space.

24. An ionic discharge amplifier comprising a sealed envelope containing mercury vapor, a thermionic emission cathode, a wound control grid encircling said cathode along its emission length and positioned at a distance from the cathode no greater than the cathode fall space of said mercury vapor, the number of turns of said grid being substantially not less than twenty-eight to the inch nor substantially more than thirty-six to the inch, a wound electrostatically shielding electrode encircling said con trol grid and being closely spaced therefrom, said shielding electrode and said control grid having approximately the same number of turns, a nickel anode surrounding said cathode, control grid and shielding electrode, said anode being positioned at a distance from the cathode greater than the said cathode fall space, and mica blocking members positioned over the anode terminals for confining the discharge to the space between the cathode and anode.

SAMUEL RUBEN. 

